A rotary body unit including two rotary bodies is known in the art. One example of a conventional rotary body unit includes a photosensitive drum (first rotary body) functioning as a drive roller, and a cleaning roller (second rotary body) functioning as a follow roller that rotates along with the photosensitive drum. The photosensitive drum has a drive-force receiving part for receiving a drive force inputted from an external source, and a first gear provided on the end portion of the drum. The cleaning roller has a second gear engaged with the first gear of the photosensitive drum and rotates along with the photosensitive drum by a drive force transmitted from the first gear.